Investigators have told news agencies today that a sailor has been charged with setting off the fire extinguishing system on the Russian nuclear submarine Nerpa, causing the deaths of 20 people.

“The inquiry has established that a member of the crew, a sailor, set off the anti-fire system on board the submarine, without authorization and for no reason,” investigator Vladimir Markin was quoted as saying by RIA-Novosti.

“This sailor has already admitted his error,” said Markin, a spokesman for the inquiry panel looking into Saturday’s deadly accident in the Sea of Japan that raised new doubts about the safety of Russian military hardware. “In connection with this, the suspect faces charges… of negligence leading to the death or two or more people.”

The sailor faces a maximum sentence of seven years in prison for his role in the incident, which killed 20 people and led to the hospitalization of 21 others, RIA Novosti said.